Hybrid cars or other devices include a booster circuit in a system for supplying power to a motor. A reactor is used as a component of the booster circuit. An example of such a reactor is disclosed in Patent Literature 1.
As illustrated in FIG. 7, the reactor disclosed in Patent Literature 1 includes a coil 105, inner cores 101c disposed inside the coil 105, and outer cores 101e disposed so as to be exposed outside the coil 105. More specifically, as illustrated in FIG. 8, the coil 105 is constituted by a pair of coil elements 105a and 105b that are connected to each other and arranged side by side, the coil elements 105a and 105b being formed by helically winding a wire 105w. The inner cores 101c are pillars each having a rectangular cross section and are individually disposed inside the coil elements 105a and 105b. The outer cores 101e are exposed outside the coil 105 and are pillars of a substantially trapezoidal (trapezoid-like) shape having upper and lower bases. The outer cores 101e face end surfaces of the inner cores 101c to form an annular core. These components are integrated from the left and right sides of FIG. 8 so as to form a reactor 100 illustrated in FIG. 7.
The outer core 101e is made of coated soft magnetic powder, which includes multiple soft magnetic particles formed by coating soft magnetic particles with insulating coated films, as raw-material powder and formed by compacting the raw-material powder. Generally, compacting is performed by filling a compacting space, which is defined by a pillar-like first punch and a tubular die, with coated soft magnetic powder and compressing the coated soft magnetic powder in the compacting space by using the first punch and a pillar-like second punch, the first punch and the die being movable relative to each other. At this time, the coated soft magnetic powder is compressed so that the first punch and the second punch form upper and lower surfaces of an outer core. This is because compacting of a dust compact is generally performed by compressing raw-material powder such that the obtained compact has a uniform cross section when taken in a direction orthogonal to the pressure-application direction.